U.S. patent application number 12/999387 was filed with the patent office on 2011-04-28 for absorption medium and method for removing sour gases from fluid streams, in particular from flue gases.
This patent application is currently assigned to BASF SE. Invention is credited to Hugo Rafael Garcia Andarcia, Ute Lichtfers, Georg Sieder, Oliver Spuhl, Robin Thiele, Susanna Voges.
Application Number | 20110094381 12/999387 |
Document ID | / |
Family ID | 40911946 |
Filed Date | 2011-04-28 |
United States Patent
Application |
20110094381 |
Kind Code |
A1 |
Lichtfers; Ute ; et
al. |
April 28, 2011 |
ABSORPTION MEDIUM AND METHOD FOR REMOVING SOUR GASES FROM FLUID
STREAMS, IN PARTICULAR FROM FLUE GASES
Abstract
Absorption medium for acid gases comprising an oligoamine (A) of
the general formula (I) ##STR00001## and a piperazine derivative
(B) of the general formula (II) ##STR00002## in which the weight
ratio of oligoamine (A) to the piperazine derivative (B) is 0.2 to
25, and also process for removing acid gases from a gas stream by
contacting the gas stream at a pressure of 0.05 to 10 MPa abs with
an aqueous solution of said absorption medium which is brought to
and maintained at a temperature of 20 to 80.degree. C.
Inventors: |
Lichtfers; Ute; (Karlsruhe,
DE) ; Thiele; Robin; (Speyer, DE) ; Voges;
Susanna; (Ludwigshafen, DE) ; Sieder; Georg;
(Bad Durkheim, DE) ; Spuhl; Oliver; (Mannheim,
DE) ; Andarcia; Hugo Rafael Garcia; (Mannheim,
DE) |
Assignee: |
BASF SE
Ludwigshafen
DE
|
Family ID: |
40911946 |
Appl. No.: |
12/999387 |
Filed: |
June 9, 2009 |
PCT Filed: |
June 9, 2009 |
PCT NO: |
PCT/EP2009/057101 |
371 Date: |
December 16, 2010 |
Current U.S.
Class: |
95/187 ; 252/184;
95/236 |
Current CPC
Class: |
B01D 2257/504 20130101;
Y02C 10/06 20130101; B01D 53/1493 20130101; C10L 3/102 20130101;
B01D 53/1475 20130101; B01D 2251/80 20130101; C10L 3/10 20130101;
Y02C 20/40 20200801; B01D 2253/102 20130101 |
Class at
Publication: |
95/187 ; 252/184;
95/236 |
International
Class: |
B01D 53/14 20060101
B01D053/14; C09K 3/00 20060101 C09K003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 23, 2008 |
EP |
08158768.5 |
Apr 24, 2009 |
EP |
09158689.1 |
Claims
1. An absorption medium for acid gases which comprises (A) an
oligoamine of the general formula (I) ##STR00007## in which R.sup.1
is C.sub.1- to C.sub.3-alkyl, R.sup.2 is hydrogen or C.sub.1- to
C.sub.3-alkyl, n is 2 to 6, and p is 1 to 3; and (B) a piperazine
derivative of the general formula (II) ##STR00008## in which
R.sup.a is hydrogen, C.sub.1- to C.sub.3-alkyl,
--CH.sub.2CH.sub.2OH or --(CH.sub.2).sub.mNH.sub.2 where m is 1 to
3, and R.sup.b is hydrogen, C.sub.1- to C.sub.3-alkyl or
--(CH.sub.2).sub.nNH.sub.2 where n is 1 to 3, R.sup.c is hydrogen,
C.sub.1- to C.sub.3-alkyl or --(CH.sub.2).sub.oNH.sub.2 where o is
1 to 3, R.sup.d is hydrogen, C.sub.1- to C.sub.3-alkyl or
--(CH.sub.2).sub.pNH.sub.2 where p is 1 to 3, and R.sup.e is
hydrogen, C.sub.1- to C.sub.3-alkyl or --(CH.sub.2).sub.qNH.sub.2
where q is 1 to 3, wherein the weight ratio of oligoamine (A) to
the piperazine derivative (B) m[oligoamine (A)]/m[piperazine
derivative (B)] is 0.2 to 25.
2. The absorption medium for acid gases according to claim 1, in
which the weight ratio of oligoamine (A) to the piperazine
derivative (B) m[oligoamine (A)]/m[piperazine derivative (B)] is
0.2 to 4.
3. The absorption medium for acid gases according to claim 1, in
which the concentration of oligoamine (A) plus piperazine
derivative (B) is 10 to 60% by weight. based on the total amount of
the absorption medium.
4. The absorption medium for acid gases according to claim 1, in
which the concentration of oligoamine (A) is between 1 and 20% by
weight, based on the total amount of the absorption medium.
5. The absorption medium for acid gases according to claim 1, in
which the oligoamine (A) is bis(3-dimethylaminopropyl)amine.
6. The absorption medium for acid gases according to claim 1, in
which the piperazine derivative (B) is piperazine.
7. The absorption medium for acid gases according to claim 1,
further comprising water, wherein the weight ratio of the sum of
oligoamine (A) plus piperazine derivative (B) to water
{m[oligoamine (A)]+m[piperazine derivative (B)]}/m[water] is 0.11
to 1.5.
8. A process for removing acid gases from a gas stream by
contacting the gas stream at a pressure of 0.05 to 10 MPa abs with
a liquid absorption medium which is brought to and maintained at a
temperature of 20 to 80.degree. C. which comprises using as liquid
absorption medium an absorption medium for acid gases according to
claim 7.
9. The process according to claim 8, wherein the acid gas is
removed in a scrubbing column operated in countercurrent flow, in
which, in the interior, a discontinuous liquid phase forms, in the
presence of activated carbon that is present in the interior of the
scrubbing column.
10. The process according to claim 8, wherein biogas or flue gas is
used and the process is carried out at a pressure of 0.05 to 0.5
MPa abs.
11. The process according to claim 8, wherein the gas stream
comprises 0.1 to 21% by volume of oxygen.
12. The process according to claim 8, wherein the acid gas
comprises carbon dioxide and the carbon dioxide concentration in
the gas stream is 0.1 to 50% by volume.
13. The process according to claim 8, wherein the absorption medium
which is loaded with carbon dioxide after being contacted with the
gas stream is regenerated by heating, by expansion, by stripping
with an inert fluid, or a combination of two or all three of said
measures.
14. The absorption medium for acid gases according to claim 2, in
which the concentration of oligoamine (A) plus piperazine
derivative (B) is 10 to 60% by weight, based on the total amount of
the absorption medium.
15. The absorption medium for acid gases according to claim 2, in
which the concentration of oligoamine (A) is between 1 and 20% by
weight, based on the total amount of the absorption medium.
16. The absorption medium for acid gases according to claim 3, in
which the concentration of oligoamine (A) is between 1 and 20% by
weight, based. on the total amount of the absorption medium.
17. The absorption medium for acid gases according to claim 2, in
which the oligoamine (A) is bis(3-dimethylaminopropyl)amine.
18. The absorption medium for acid gases according to claim 3, in
which the oligoamine (A) is bis(3-dimethylaminopropyl)amine.
19. The absorption medium for acid gases according to claim 4, in
which the oligoamine (A) is bis(3-dimethylaminopropyl)amine.
20. The absorption medium for acid gases according to claim 2, in
which the piperazine derivative (B) is piperazine.
Description
[0001] The present invention relates to an absorption medium for
acid gases comprising an oligoamine (A) and a piperazine derivative
(B) in which the weight ratio of oligoamine (A) to the piperazine
derivative (B) is 0.2 to 25. In addition, the present invention
relates to a process for removing acid gases from a gas stream by
contacting the gas stream at a pressure of 0.05 to 10 MPa abs with
an aqueous solution of said absorption medium heated to and
maintained at a temperature of 20 to 80.degree. C.
[0002] The removal of acid gases such as, e.g., CO.sub.2, H.sub.2S,
SO.sub.2, COS, CS.sub.2, HCN or mercaptans, from fluid streams,
such as natural gas, refinery gas, synthesis gas, is of importance
for differing reasons. Carbon dioxide must be removed from natural
gas, for example, since a high carbon dioxide concentration reduces
the calorific value of the gas. In addition, carbon dioxide in
combination with moisture which is frequently entrained in the
fluid streams can lead to corrosion in pipes and fittings. In
addition, the content of sulfur compounds in the natural gas must
also be reduced by suitable treatment measures, since the sulfur
compounds, in the water which is frequently entrained by the
natural gas, also form acids which act corrosively. Therefore, for
the transport of natural gas in a pipeline, preset limiting values
of the sulfur-comprising impurities must be complied with. In
addition, numerous sulfur compounds are foul-smelling, even at low
concentrations, and, especially sulfur dioxide, toxic.
[0003] The removal of carbon dioxide from combustion exhaust gases
or flue gases is desirable, in particular for decreasing the
emission of carbon dioxide, which is considered to be the main
cause of what is termed the greenhouse effect. Flue gases generally
have a carbon dioxide partial pressure of 10 to 500 hPa.
Customarily these occur at a pressure close to atmospheric
pressure. In order to achieve an effective removal of carbon
dioxide, the absorption medium must have a high carbon dioxide
affinity. The high carbon dioxide affinity, on the other hand, has
the effect that, in the regeneration of the absorption medium, the
carbon dioxide is generally not completely expelled and the
regenerated absorption medium has a carbon dioxide residual
loading. Only the difference between the maximum load capacity of
the absorption medium and the residual loading of the regenerated
absorption medium is available as cycle capacity.
[0004] One absorption medium which is particularly approved in
practice for removing acid gases from, for example, synthesis gas,
natural gas or biogas is described in U.S. Pat. No. 4,336,233. This
is an aqueous solution of methyldiethanolamine (MDEA) and
piperazine as activator for increasing the absorption rate. The
described absorption medium comprises 1.5 to 4.5 mol/l of
methyldiethanolamine and 0.05 to 0.8 mol/l of piperazine.
[0005] EP-A 0 879 631 describes a process for removing carbon
dioxide from a combustion gas by contacting the combustion gas at
atmospheric pressure with an aqueous amine solution. The amine
solution comprises one secondary amine and one tertiary amine, each
at a concentration of 10 to 45% by weight.
[0006] U.S. Pat. No. 6,165,433 relates to carbon dioxide removal
from a gas stream, the carbon dioxide partial pressure of which is
10 psia (689 hPa) or less using an absorption medium which
comprises water, 5 to 35% by weight of a fast-reaction-rate amine
and 5 to 50% by weight of a slow-reaction-rate amine.
Fast-reaction-rate amines are monoethanolamine, diethanolamine,
piperazine and diisopropanolamine. Slow-reaction-rate amines are
methyldiethanolamine, triethanolamine, and sterically hindered
amines such as 2-amino-2-methyl-1-propanol.
[0007] WO 2005/087,350 discloses a process for removing carbon
dioxide from flue gases using a liquid absorption medium which
comprises a tertiary aliphatic amine and an activator such as
3-methylaminopropylamine. The tertiary aliphatic amine should have
a reaction enthalpy .DELTA..sub.RH of the protonation reaction
which is greater than that of methyldiethanolamine. The absorption
medium comprises 20 to 60% by weight of tertiary aliphatic amine
and 1 to 10% by weight of activator.
[0008] Frequently, alkanolamines are used for removing carbon
dioxide from flue gases.
[0009] WO 02/007,862 describes a process and an absorption medium
for removing acid gases from a fluid stream. The absorption medium
comprises a tertiary aliphatic alkanolamine and an activator such
as 3-methylaminopropylamine. The treatment of fluid streams having
low carbon dioxide partial pressures is not described.
[0010] WO 2007/144,372 describes a process for removing carbon
dioxide from flue gases by contacting them with an aqueous solution
of a tertiary aliphatic alkanolamine and an N-alkyldiamine which is
specified in more detail. As preferred tertiary aliphatic
alkanolamines, methyldiethanolamine, methyldiisopropanolamine and
butyldiethanolamine are mentioned. As preferred activator, in
particular 3-methylaminopropylamine is mentioned.
[0011] In particular, in industrial processes for removing carbon
dioxide from flue gases, preferably use is made of monoethanolamine
(MEA) as absorption medium. Thus, for instance, Satish Reddy et al.
of Fluor Corporation, in an abstract for the Second National
Conference on Carbon Sequestration of the National Energy
Technology Laboratory/Department of Energy, Alexandria, Va.,
U.S.A., which took place from the 5th to 8th of May 2003 with the
title "Fluor's Econamine FG Plus.sup.SM Technology--An enhanced
amine-based CO.sub.2 capture process", describe the removal of
carbon dioxide from flue gases using an absorption medium
comprising monoethanolamine and a secret inhibitor. The latter
suppresses the degeneration of monoethanolamine due to the presence
of oxygen and at the same time protects the plant from corrosion.
This process, at the time of publication, was already being used in
23 commercially operated plants.
[0012] Technologies based on monoethanolamine are distinguished by
a high reactivity between the amine and carbon dioxide. However,
the high reactivity is disadvantageously accompanied by a high
absorption enthalpy and a high energy requirement for regeneration.
Other alkanolamines such as, for instance, diethanolamine or
methyldiethanolamine, which have a lower energy requirement for
regeneration, are suitable only with restrictions for this
separation task owing to their slower reaction kinetics between
carbon dioxide and amine.
[0013] WO 99/004,885 teaches the removal of acid gases from a gas
stream by contacting them with an aqueous solution of an oligoamine
which is specified in more detail which has a concentration of 20
to 60% by weight and preferably comprises an alkali metal compound
or an aliphatic or cycloaliphatic mono- or diamine as activator.
Activators which are mentioned by name are sodium hydroxide, sodium
hydrogencarbonate, triethylenediamine, dicyclohexylamine,
N-ethylcyclohexylamine and N,N-dimethylcyclohexylamine. A
disadvantage of the use of sodium hydroxide and sodium
hydrogencarbonate as activator is the significantly increased
energy requirement in regeneration. A disadvantage of the use of
triethylenediamine is its slow reaction kinetics which are
accompanied by a relatively long residence time or a larger
exchanger area in absorption. A disadvantage of the use of
dicyclohexylamine, N-ethylcyclohexylamine and
N,N-dimethylcyclohexylamine is their restricted miscibility with
water which limits the flexibility in adaptation of the activator
content.
[0014] The object of the present invention was to find an
absorption medium for acid gases and a process for removing acid
gases from fluid streams which does not have said disadvantages of
the prior art, or has them only to a reduced extent, and which
enables, in particular compared with the known processes using
monoethanolamine, a higher cycle capacity and a lower regeneration
requirement and simultaneously has sufficiently rapid reaction
kinetics between carbon dioxide and the amine.
[0015] Accordingly, an absorption medium for acid gases has been
found which comprises
[0016] (A) an oligoamine of the general formula (I)
##STR00003## [0017] in which [0018] R.sup.1 is hydrogen or C.sub.1-
to C.sub.3-alkyl, [0019] R.sup.2 is hydrogen or C.sub.1- to
C.sub.3-alkyl, [0020] n is 2 to 6, and [0021] p is 1 to 3; and
[0022] (B) a piperazine derivative of the general formula (II)
##STR00004## [0023] in which [0024] R.sup.a is hydrogen, C.sub.1-
to C.sub.3-alkyl, --CH.sub.2CH.sub.2OH or
--(CH.sub.2).sub.mNH.sub.2 where m is 1 to 3, and [0025] R.sup.b is
hydrogen, C.sub.1- to C.sub.3-alkyl or --(CH.sub.2).sub.nNH.sub.2
where n is 1 to 3, [0026] R.sup.c is hydrogen, C.sub.1- to
C.sub.3-alkyl or --(CH.sub.2).sub.oNH.sub.2 where o is 1 to 3,
[0027] R.sup.d is hydrogen, C.sub.1- to C.sub.3-alkyl or
--(CH.sub.2).sub.pNH.sub.2 where p is 1 to 3, and [0028] R.sup.e is
hydrogen, C.sub.1- to C.sub.3-alkyl or --(CH.sub.2).sub.qNH.sub.2
where q is 1 to 3, wherein the weight ratio of oligoamine (A) to
the piperazine derivative (B) m[oligoamine (A)]/m[piperazine
derivative (B)] is 0.2 to 25.
[0029] Examples of suitable oligoamines (A) which may be mentioned
are diethylenetriamine, bis(3-methylaminopropyl)methylamine,
dimethyldipropylenetriamine, dipropylenetriamine,
N,N',N''-trimethylbis(hexamethylene)triamines and
bis(3-dimethylaminopropyl)amine. Preference is given to an
oligoamine (A) of the general formula (I) in which R.sup.1 is
hydrogen or methyl, R.sup.2 is hydrogen or methyl, n is 2 or 3, and
p is 1. Particular preference is given to diethylenetriamine,
bis(3-methylaminopropyl)methylamine, dimethyldipropylenetriamine,
dipropylene-triamine, and bis(3-dimethylaminopropyl)amine, in
particular bis(3-dimethylaminopropyl)amine (R.sup.1 is methyl,
R.sup.2 is hydrogen, n is 3 and p is 1).
[0030] Preference is given to a piperazine derivative (B) of the
general formula (II) in which [0031] R.sup.a is hydrogen,, methyl,
ethyl, --CH.sub.2CH.sub.2OH or --CH.sub.2CH.sub.2NH.sub.2. [0032]
R.sup.b is hydrogen or methyl, [0033] R.sup.c is hydrogen or
methyl, R.sup.d is hydrogen or methyl, and [0034] R.sup.e is
hydrogen or methyl.
[0035] As particularly preferred piperazine derivatives (B),
mention may be made of piperazine, N-hydroxyethylpiperazine,
N-aminoethylpiperazine, 2-methylpiperazine and
2,5-dimethylpiperazine. Very particular preference is given to
piperazine (R.sup.a to R.sup.e are hydrogen).
[0036] The weight ratio of oligoamine (A) to the piperazine
derivative (B)
m[oligoamine (A)]/m[piperazine derivative (B)]
in the absorption medium according to the invention is 0.2 to 25,
preferably 0.2 to 4, and particularly preferably 0.3 to 2.
[0037] On the basis of the total amount of the absorption medium,
the concentration of oligoamine (A) plus piperazine derivative (B)
is particularly advantageously 10 to 60% by weight, and in
particular 20 to 50% by weight.
[0038] The concentration of oligoamine (A) is preferably 1 to 20%
by weight, particularly preferably 1 to 18% by weight, and very
particularly preferably 10 to 18% by weight, based on the total
amount of the absorption medium.
[0039] Particularly advantageously, the absorption medium comprises
in addition water, and the weight ratio of the sum of oligoamine
(A) plus piperazine derivative (B) to water
{m[oligoamine (A)]+m[piperazine derivative (B)]}/m[water]
is preferably 0.11 to 1.5 and particularly preferably 0.25 to
1.
[0040] The absorption medium can in addition additionally comprise
physical solvents. A physical solvent is taken to mean a solvent
which enters into only a relatively weak interaction with the acid
gas. Examples of suitable physical absorption media which are also
customary in practice are, for instance, cyclotetramethylene
sulfone (sulfolane) and derivatives thereof, aliphatic acid amides
(e.g. acetylmorpholine, N-formylmorpholine), N-alkylated
pyrrolidones and piperidones (e.g. N-methylpyrrolidone), propylene
carbonate, methanol or dialkyl ethers of polyethylene glycols.
[0041] In addition, a process has been found for removing acid
gases from a gas stream by contacting the gas stream at a pressure
of 0.05 to 10 MPa with a liquid absorption medium which is brought
to and maintained at a temperature of 20 to 80.degree. C., which
comprises using as liquid absorption medium an absorption medium
which comprises
[0042] (A) an oligoamine of the general formula (I)
##STR00005## [0043] in which [0044] R.sup.1 is hydrogen or C.sub.1-
to C.sub.3-alkyl, [0045] R.sup.2 is hydrogen or C.sub.1- to
C.sub.3-alkyl, [0046] n is 2 to 6, and [0047] p is 1 to 3; and
[0048] (B) a piperazine derivative of the general formula (II)
##STR00006## [0049] in which [0050] R.sup.a is hydrogen, C.sub.1-
to C.sub.3-alkyl, --CH.sub.2CH.sub.2OH or
--(CH.sub.2).sub.mNH.sub.2 where m is 1 to 3, and [0051] R.sup.b is
hydrogen, C.sub.1- to C.sub.3-alkyl or --(CH.sub.2).sub.nNH.sub.2
where n is 1 to 3, [0052] R.sup.c is hydrogen, C.sub.1- to
C.sub.3alkyl or --(CH.sub.2).sub.oNH.sub.2 where o is 1 to 3,
[0053] R.sup.d is hydrogen, C.sub.1- to C.sub.3-alkyl or
--(CH.sub.2).sub.pNH.sub.2 where p is 1 to 3, and [0054] R.sup.e is
hydrogen, C.sub.1- to C.sub.3-alkyl or --(CH.sub.2).sub.qNH.sub.2
where q is 1 to 3, and
[0055] (C) water
wherein the weight ratio of oligoamine (A) to the piperazine
derivative (B)
m[oligoamine (A)]/m[piperazine derivative (B)]
is 0.2 to 25 and the weight ratio of the sum of oligoamine (A) plus
piperazine derivative (B) to water
{m[oligoamine (A)]+m[piperazine derivative (B)]}/m[water]
is 0.11 to 1.5.
[0056] It is preferred to use in the process according to the
invention the preferred absorption media mentioned in the
description of the absorption medium.
[0057] The absorption of the acid gas proceeds in this case by
contacting the gas stream which is to be purified with the liquid
absorption medium in a suitable device. Suitable devices comprise
at least one scrubbing column which can be designed, for example,
as a dumped-bed packed column, arranged packing column or tray
column and/or other absorbers such as, for example, a membrane
contactor, a radial flow scrubber, a jet scrubber, a venturi
scrubber or a rotary spray scrubber. However, the gas stream is
treated with the absorption medium preferably in a scrubbing
column. This is particularly advantageously operated in
countercurrent flow. The gas stream in this case is generally fed
into the lower region of the column and the absorption medium into
the upper region of the column.
[0058] The contacting in the process according to the invention
proceeds at a pressure of 0.05 to 10 MPa abs. The liquid absorption
medium in this case is brought to and maintained at a temperature
of 20 to 80.degree. C., preferably with respect to the lower limit,
to a temperature of greater than or equal to 30.degree. C., and
with respect to the upper limit to a temperature of less than or
equal to 60.degree. C. The gas on entry into the separation device
generally has a temperature of 20 to 80.degree. C., preferably 30
to 60.degree. C.
[0059] In an advantageous embodiment, the acid gas is removed in a
scrubbing column operated in countercurrent flow, in which, in the
interior, a discontinuous liquid phase forms, in the presence of
activated carbon that is present in the interior of the scrubbing
column. The scrubbing column to be used in addition comprises the
customarily used internals such as, for example, random packing
elements or ordered packings. The activated carbon has a carbon
content preferably of greater than 90% by weight and a BET surface
area of 300 to 2000 m.sup.2/g. The concentration thereof is
generally 1 to 2000 g of activated carbon per m.sup.3 volume of the
scrubbing column. The activated carbon can be fed in various ways.
In a preferred embodiment, it is suspended in the liquid absorption
medium. In this case its particle size is preferably in the range
from 0.1 to 1000 .mu.m, particularly preferably 0.1 to 50 .mu.m.
Based on the liquid absorption medium, the concentration of the
suspended activated carbon is preferably 0.01 to 20 kg per m.sup.3,
particularly preferably 1 to 10 kg per m.sup.3. In another
preferred embodiment, it is applied in a spatially fixed form
within the scrubbing column. In this case the activated carbon is
situated, for example, in fixed liquid-permeable and gas-permeable
pockets (for instance in the form of activated carbon pellets) or
in the form of activated carbon-coated packings or random packing
elements fixed in the scrubbing column. Based on the volume of the
scrubbing column, the concentration of the fixed activated carbon
is preferably 1 g to 2 kg per m.sup.3, particularly preferably 100
g to 1 kg per m.sup.3. Owing to the presence of activated carbon,
the absorption rate of the liquid absorption medium is increased,
which leads to a still more effective process procedure. Further
details on using activated carbon in the absorption of acid gases
in aqueous alkaline absorption media are described in the European
priority publication having the application number EP 09 154
427.0.
[0060] The acid gas can be liberated from the absorption medium
which is loaded with the acid gas in a regeneration step, wherein a
regenerated absorption medium is obtained. In the regeneration step
the loading of the absorption medium is decreased and the resultant
regenerated absorption medium is preferably subsequently
recirculated to the absorption step.
[0061] Generally, the loaded absorption medium is regenerated by
heating (for example to 70 to 110.degree. C.), by expansion and/or
by stripping with an inert fluid, or a combination of two or all
three of said measures. An inert fluid is taken to mean a gas which
does not react chemically either with the absorption medium or with
the acid gas and also does not dissolve in the absorption medium,
or dissolves at most to an insignificant extent. Suitable inert
fluids which may be mentioned are, for example, nitrogen, water
vapor or air.
[0062] Generally, the loaded absorption medium is heated for
regeneration and the liberated acid gas is separated off, for
example in a desorption column. Before the regenerated absorption
medium is reintroduced into the absorber, it is cooled to a
suitable absorption temperature. In order to utilize the energy
present in the hot regenerated absorption medium, it is preferred
to preheat the loaded absorption medium from the absorber by heat
exchange with the hot regenerated absorption medium. By means of
the heat exchange the loaded absorption medium is brought to a
higher temperature and so in the regeneration step a lower energy
input is required. By means of the heat exchange, possibly, a
partial regeneration of the loaded absorption medium can also
already proceed with liberation of acid gas. The resultant
gas-liquid mixed-phase stream is then passed in this case into a
phase separation vessel from which the acid gas is taken off. The
liquid phase, for complete regeneration of the absorption medium,
is passed into the desorption column.
[0063] As gas streams from which the acid gases are to be removed,
use can be made of in principle all natural and synthetic,
oxygen-comprising and oxygen-free gas streams such as, for example,
natural gas, refinery gases, synthesis gases, biogases or flue
gases. The process according to the invention proceeds, when
natural gases are used, preferably at a pressure of 3 to 10 MPa
abs, when refinery gases are used, preferably at a pressure of 0.05
to 10 MPa abs, when synthesis gases are used preferably at a
pressure of 1.5 to 6 MPa abs, and when biogases or flue gases are
used, preferably at a pressure of 0.05 to 0.5 MPa abs.
[0064] Very particularly preferably, the process according to the
invention is the removal of carbon dioxide from oxygen-comprising
gas streams. These comprise preferably 0.1 to 21% by volume of
oxygen. Preferred oxygen-comprising gas streams which may be
mentioned, in particular, are [0065] combustion gases or flue gases
which are obtained by the combustion of organic substances; [0066]
gases from the composting or storage of organic substances,
including organic waste materials; and [0067] gases from the
bacterial decomposition of organic substances.
[0068] Acid gases are taken to mean compounds which occur in the
gaseous state under the available conditions in the gas stream
which is to be purified and, in aqueous solution, have a pH of
<7. Typical acid gases are, for example, carbon dioxide
(CO.sub.2), hydrogen sulfide (H.sub.2S), sulfur dioxide (SO.sub.2),
carbonyl sulfide (COS), carbon disulfide (CS.sub.2), hydrogen
cyanide (HCN) and mercaptans (RSH). The process according to the
invention removes preferably carbon dioxide and hydrogen sulfide,
and particularly preferably carbon dioxide. The carbon dioxide
concentration in the gas stream preferably used is therefore
preferably 0.1 to 50% by volume.
[0069] Generally, the preferred gas streams comprise less than 100
mg/m.sup.3 (S.T.P.) of sulfur dioxide and preferably less than 50
mg/m.sup.3 (S.T.P.) of sulfur dioxide. In addition the preferred
gas streams generally comprise less than 100 mg/m.sup.3 (S.T.P.) of
nitrogen oxides, and preferably less than 50 mg/m.sup.3 (S.T.P.) of
nitrogen oxides.
[0070] Hereinafter, by way of example and without being
restrictive, a possible procedure in the removal of carbon dioxide
from flue gases using the process according to the invention is
described. Before the absorption of carbon dioxide according to the
invention, the flue gas is preferably subjected to a scrubbing with
an aqueous liquid, in particular with water, in order to cool and
moisten (quench) the flue gas. During this scrubbing, dusts or
gaseous impurities such as sulfur dioxide can also be removed.
[0071] The pretreated flue gas is then fed to the actual carbon
dioxide removal. FIG. 1 shows in this context a schematic drawing
of a plant suitable for carrying out the process according to the
invention. Therein the symbols hereinafter have the following
meanings: [0072] 1=flue gas [0073] 2=flue gas depleted in carbon
dioxide [0074] 3=separated carbon dioxide [0075] A=absorption
column [0076] B=water scrubbing [0077] C=absorption [0078] D=cooler
[0079] E=cooler [0080] F=pump [0081] G=pump [0082] H=desorption
column [0083] I=heat exchanger [0084] J=evaporator (reboiler)
[0085] K=condenser
[0086] According to FIG. 1, flue gas 1 is passed into the lower
part of the absorption column A and brought into contact with the
absorption medium in countercurrent flow. The flue gas depleted in
carbon dioxide is further scrubbed with water in the upper part of
the absorption column and passed out of the column overhead as
stream 2. The absorption medium which is loaded with carbon dioxide
is withdrawn at the bottom of the absorption column A and fed into
the desorption column H via the pump G and the heat exchanger I. In
the lower part of the desorption column, the loaded absorption
medium is heated via the evaporator J. By means of the temperature
elevation some of the absorbed carbon dioxide converts back into
the gas phase. This is removed at the top of the desorption column
H and cooled in the condenser K. Absorption medium which is
condensed out is recirculated overhead. The gaseous carbon dioxide
is withdrawn as stream 3. The regenerated absorption medium is
recirculated back to the absorption column A via the pump F and the
cooler E.
[0087] The absorption medium according to the invention
surprisingly exhibits very balanced properties with respect to the
absorption rate which is astonishingly very high and with respect
to the energy requirement for regeneration which is astonishingly
very low. Therefore, owing to the high absorption rate the use of a
relatively small absorption column is possible, since a smaller
exchange area or a shorter residence time is absolutely sufficient.
Likewise, the evaporator (reboiler) for the desorption column can
also be designed so as to be smaller since less energy is required
for regenerating the absorption medium. By means of the high
absorption rate, by means of the absorption medium according to the
invention, a high cycle capacity can also be achieved.
EXAMPLES
Example 1
Relative Cycle Capacity and Relative Steam Requirement for
Regeneration in the Case of Absorption Media According to the
Invention and Not According to the Invention
[0088] For determination of the carbon dioxide cycle capacity and
the regeneration requirement, laboratory experiments were carried
out using various absorption media loaded with carbon dioxide. As
comparison base, 30% by weight of monoethanolamine (MEA) in water
was used. The absorption medium according to the invention
comprised 15% by weight of bis(3-dimethylaminopropyl)amine
(bisDMAPA) and 15% by weight of piperazine.
[0089] For determination of the relative cycle capacity and
estimation of the relative steam requirement for regeneration of
the absorption medium, the equilibrium loadings of carbon dioxide
in the absorption medium were determined as a function of carbon
dioxide partial pressure at 40.degree. C. (for the absorber bottom)
and at 120.degree. C. (for the desorber bottom). These measurements
were carried out for all systems listed in Table 1. For
determination of the equilibrium loading, a glass pressure vessel
having a volume of approximately 100 cm.sup.3 was used. In this, a
defined amount of the absorption medium was charged, the vessel was
evacuated and at constant temperature carbon dioxide was added
stepwise via a defined gas volume. The amount of carbon dioxide
dissolved in the liquid phase was calculated taking into account
the gas space correction due to the overlying gas phase.
[0090] The following assumptions were made for estimating the cycle
capacity of the absorption medium: [0091] 1. The absorber is
charged at a total pressure of 1 bar with a carbon
dioxide-comprising flue gas having a carbon dioxide partial
pressure of 130 hPa (corresponding approximately to 13% by volume
of carbon dioxide in the flue gas at atmospheric pressure). [0092]
2. In the absorber bottom a temperature of 40.degree. C. prevails.
[0093] 3. During the regeneration in the desorber bottom a
temperature of 120.degree. C. prevails. [0094] 4. In the absorber
bottom an equilibrium state is achieved. The carbon dioxide
equilibrium partial pressure is therefore equal to the feed gas
partial pressure of 130 hPa. [0095] 5. During the desorption a
carbon dioxide partial pressure of 100 hPa prevails in the desorber
bottom. [0096] 6. During the desorption an equilibrium state is
achieved.
[0097] The capacity of the absorption medium was determined from
the loading (in m.sup.3 (S.T.P.) of carbon dioxide/t of absorption
medium) at the point of intersection of the 40.degree. C.
equilibrium curve with the line of constant feed gas carbon dioxide
partial pressure of 13 kPa (loaded solution at the absorber bottom
in equilibrium) and from the loading at the point of intersection
of the 120.degree. C. equilibrium curve with the line of constant
partial pressure of 100 hPa (regenerated solution at the desorber
bottom in equilibrium). The difference between the two loadings is
the cycle capacity of the respective solvent. A high capacity means
that less solvent needs to be circulated and therefore the
apparatuses such as, for example, pumps, heat exchangers and also
piping can be dimensioned so as to be smaller. In addition, the
circulation rate also affects the energy required for
regeneration.
[0098] A further index of the application properties of an
absorption medium is the gradient of the operating lines in the
McCabe-Thiele diagram of the desorber. For the conditions in the
bottom of the desorber, the operating line is generally very close
to the equilibrium line, and so the gradient of the equilibrium
curve can be considered to be approximately equal to the gradient
of the operating lines. At a constant liquid loading, for
regeneration of an absorption medium having a high gradient of the
equilibrium curve, a lower amount of stripping steam is required.
The energy requirement for generating the stripping steam is an
important contributor to the total energy requirement of the carbon
dioxide absorption process.
[0099] Expediently, the reciprocal value of the gradient is
reported, since this is directly proportional to the amount of
steam required by kilogram of absorption medium. If the reciprocal
value is divided by the capacity of the absorption medium, this
gives a comparison value which directly enables a relative
statement on the required amount of steam per amount of carbon
dioxide absorbed.
[0100] In Table 1, the values of the relative cycle capacity and
the relative steam requirement, normalized to MEA, are shown for
the absorption medium according to the invention. In comparison
with 30% by weight of MEA, the relative cycle capacity increases to
128% when 15% by weight of bisDMAPA+15% by weight of piperazine are
used. The relative steam requirement reduces significantly to 68%.
which is an enormous potential savings in industrial
application.
Example 2
Relative Absorption Rates for Absorption Media According to the
Invention and Not According to the Invention
[0101] For determination of the mass transport rate of carbon
dioxide from the gas stream into the absorption medium,
measurements were carried out in a double stirred cell. The mass
transport rate, in the case of reactive absorption, is composed
both of the physical mass transport and the reaction kinetics
between the absorption medium and the carbon dioxide. These two
parameters can be measured as a summary parameter in the double
stirred cell. Comparison bases used were 31.2% by weight of
monoethanolamine (MEA) in water and also 30% by weight of
bis(3-dimethylaminopropyl)amine (bisDMAPA) in water. The absorption
media according to the invention comprised 15 to 28.6% by weight of
bisDMAPA and 1.4 to 15% by weight of piperazine.
[0102] FIG. 2 shows a schematic drawing of the double stirred cell
having the following elements: [0103] A=carbon dioxide reservoir
[0104] B=double stirred cell [0105] C=thermostating [0106]
D=metering valve [0107] E=pressure meter
[0108] The double stirred cell had an internal diameter of 85 mm
and a volume of 509 ml. The cell was thermostated to 50.degree. C.
during the experiments. For mixing of the gas and liquid phases,
the cell was equipped with two agitators according to the schematic
drawing. Before the start of the experiment the double stirred cell
was evacuated. A defined volume of the degassed absorption medium
was transported into the doubled stirred cell and thermostated to
50.degree. C. The agitators were already turned on during heating
up of the unloaded absorption medium. The agitator speed was
selected such that a planar phase interface is established between
the liquid phase and the gas phase. Wave formation of the phase
interface must be avoided, since as a result no defined phase
interface would be present. After the desired experimental
temperature was reached, carbon dioxide was introduced into the
reactor via a control valve. The volumetric flow rate was
controlled in such a manner that in the double stirred cell, during
the experiment, a constant pressure of 50 hPa abs (equivalent to
carbon dioxide partial pressure) prevailed. With increasing
experimental time, the volumetric flow rate of carbon dioxide
decreased, since the absorption medium became saturated with time
and therefore the absorption rate decreased. The volumetric flow
rate of carbon dioxide which flowed into the double stirred cell
was recorded over the entire experimental period. The end of the
experiment was reached as soon as carbon dioxide no longer flowed
into the double stirred cell. The absorption medium at the end of
the experiment was virtually in the equilibrium state.
[0109] For evaluation of the experiments, the absorption rate in
mole of CO.sub.2/(m.sup.3 of absorption mediummin) was determined
as a function of the loading of the absorption medium. The
absorption rate was calculated from the recorded volumetric flow
rate of carbon dioxide and the volume of absorption medium charged.
The loading was determined from the accumulated amount of carbon
dioxide which was fed to the double stirred cell and the charged
mass of absorption medium.
[0110] Table 2 shows the relative absorption rates of various
absorption media at a loading with 10 and 20 m.sup.3 (S.T.P.) of
CO.sub.2/t normalized to bisDMAPA.
[0111] In comparison with 30% by weight of bisDMAPA, the relative
absorption rate at a loading of 10 m.sup.3 (S.T.P.) of CO.sub.2 per
t of absorption medium increases to 269% when 15% by weight of
bisDMAPA+15% by weight of piperazine is used. At a loading of 20
m.sup.3 (S.T.P.) of CO.sub.2 per t of absorption medium, the
relative absorption rate in the case of said amine mixture
increases to 366%. Even in the case of an amine mixture having only
1.4% by weight of piperazine and 28.6% by weight of bisDMAPA, the
relative absorption rates are 145% (10 m.sup.3 (S.T.P.) of CO.sub.2
per t of absorption medium) and 182% (20 m.sup.3 (S.T.P.) of
CO.sub.2 per t of absorption medium). The carbon dioxide absorption
rate in the bisDMAPA/piperazine mixture is therefore up to three
times higher than when pure bisDMAPA is used in the same overall
concentration of 30% by weight of amine in aqueous solution.
[0112] In contrast, the aqueous solution of 31.2% by weight of MEA
shows the highest relative absorption rates of 378% in the case of
a loading of 10 m.sup.3 (S.T.P.) of CO.sub.2 per t of absorption
medium and 541% in the case of a loading of 20 m.sup.3 (S.T.P.) of
CO.sub.2 per t of absorption medium. However, it must be taken into
account here that according to example 1 the use of a pure MEA
solution in water has a significantly higher energy requirement
(steam amount) for regeneration compared with a bisDMAPA/piperazine
mixture.
[0113] Thus, although an aqueous MEA solution would have a very
high absorption rate, it would likewise have a very high energy
requirement in regeneration. Vice versa. an aqueous bisDMAPA
solution would have only an inadequately low absorption rate which,
on conversion to an industrial scale, would require a significantly
larger absorber column. Examples 1 and 2 verify that by using a
corresponding mixture, surprisingly a highly balanced absorption
medium is obtained which not only has a high absorption rate but
also requires very low energy demand for regeneration.
[0114] In addition, in the experiments, the effect due to addition
of activated carbon was also studied. For this purpose a mixture of
15% by weight BisDMAPA and 15% by weight of piperazine was
additionally admixed with 0.1% of activated carbon (Norit SA Super,
BET surface area 1150 m.sup.2/g) and the relative absorption rate
was determined in a similar manner to the other examples. Compared
with the mixture of 15% by weight of BisDMAPA and 15% by weight of
piperazine without activated carbon, the relative absorption rate
increases in the presence of only 0.1% by weight of activated
carbon at a loading of 10 m.sup.3 (S.T.P.) of CO.sub.2 per t of
absorption medium from 269% to 396% and at a loading of 20 m.sup.3
(S.T.P.) of CO.sub.2 per t of absorption medium of from 366% to
636%. The results therefore show a further significant increase of
the relative absorption rate due to the presence of activated
carbon.
TABLE-US-00001 TABLE 1 Relative cycle capacity and steam
requirement normalized to MEA Concentration of Relative amines
based on the cycle Relative steam Absorption medium m[oligoamine
(A)]/ {m[oligoamine (A)] + total amount capacity requirement [% in
% by weight] m[activator (B)] m[activator (B)]}/m[water] [% by
weight] [%] [%] 30% MEA -- -- 30 100 100 15% BisDMAPA + 15% 1 0.43
30 128 68 Pip MEA = monoethanolamine BisDMAPA =
bis(3-dimethylaminopropyl)amine Pip = piperazine
TABLE-US-00002 TABLE 2 Relative absorption rate of various
absorption media at a loading with 10 and 20 m.sup.3 (S.T.P.) of
CO.sub.2/t normalized to bisDMAPA Relative Relative absorption rate
absorption rate at a loading of at a loading of 10 m.sup.3 (S.T.P.)
20 m.sup.3 (S.T.P.) of Concentration of of CO.sub.2 per t of
CO.sub.2 per t of amines based on absorption absorption Absorption
medium m[oligoamine (A)]/ {m[oligoamine (A)] + the total amount
medium medium [% in % by weight] m[activator (B)] m[activator
(B)]}/m[water] [% by weight] [%] [%] 31.2% MEA -- -- 31.2 378 541
20% BisDMAPA + 10% 2 0.43 30 229 307 Pip 15% BisDMAPA + 15% 1 0.43
30 269 366 Pip 30% BisDMAPA -- -- 30 100 100 28.6% BisDMAPA + 1.4%
20.4 0.43 30 145 182 Pip 15% BisDMAPA + 15% 1 0.43 30 396 636 Pip +
0.1% AC MEA = monoethanolamine BisDMAPA =
bis(3-dimethylaminopropyl)amine Pip = piperazine AC = activated
carbon (Norit SA Super)
* * * * *